1. Field of the Invention
The present invention relates to a soil- and grass seed-free sod precursor containing grass sprigs and a non-woven bio-cellulosic fiber mat and a method of producing a soilless sod from the precursor.
2. Description of the Background
In the past, washed sod and soilless sod have been interchangeable terms. However, these materials are quite distinct. Washed sod is field-cut sod in which the soil has been mechanically removed from the turfgrass plant. In contrast, soilless sod is grown without any type of mineral soil substrate.
Washed sod technology was introduced by Warren""s Turf Nursery of Palos Park, Ill. in the 1970""s (see Turgeon, A. J., Comparative Advantages of Soilless Sod for Kentucky Bluegrass, Rasen Grun-flachen Begrunungen 8(1):13-15, 1977). This sod results from a post-harvest washing using a patented washing apparatus consisting of three motorized conveyors passing through two series of high pressure water jets. The apparatus requires three operators, and has a capacity of two 182.9 cmxc3x9741.9 cm sod strips per minute. The advantages of washed sod include: elimination of layering due to soil differences between sod source and destination, quick rooting establishment, ease of handling, and light weight for shipping. Washed sod has superior water infiltration rates as compared to traditional field-cut sods (see Casimaty, B. G., J. Neylan, J. B. Beard, 1993, Effects of Removal by Post-Harvest Hydraulic Washing on Sod Transplant Rooting of a Kentucky Bluegrass-Perennial Ryegrass Polystand and a Creeping Bentgrass Monostand, In R. N. Carrow, N. E. Christians, and R. C. Shearman (co-ed.), Int. Turfgrass Soc. Res. J., Vol. 7). However, washed sod can be expensive to produce, and soil removal can be difficult to accomplish while still maintaining sod integrity.
As an alternative to washed sod, methods of growing sod over an impervious plastic layer have been investigated. Some of these methods use soil as a substrate, while others utilize some form of natural or man-made organic fiber mat.
Baron, U.S. Pat. No. 4,364,197, used two layers of a non-woven organic fiber mat composed primarily of flax. A cool-season grass mix was seeded between the two layers.
Anton, U.S. Pat. No. 5,224,292, discloses growing grass seeds on a non-woven mat composed of hollow synthetic organic fibers. These hollow fibers can contain water-soluble plant nutrients, pesticides, algaecides, or weed controls within their matrix, thereby providing slow-release of the chemicals to enhance and/or protect growing seedlings.
Heard, U.S. Pat. No. 4,716,679, produced pre-grown turf by seeding grass on a layer of straw deposited on an impervious surface. Chamoulaud, U.S. Pat. No. 4,232,481, produced sod by applying grass seed to a finely crushed wood bark compost layer. Burns, looking for methods to decrease sod establishment times, grew sprigged xe2x80x98Tifwayxe2x80x99 bermudagrass [Cynodon dactylon (L.) Pers. x transvaalensis Burtt-Davy] on 8 mm of sewage sludge from a secondary treatment plant (see Burns, R. E., 1980, Techniques for Rapid Sod Production, pp. 361-366, In J. B. Beard (ed.), Proc. 3rd Int. Turfgrass Res. Conf., Munich Germany, 11-13 July 1977, Int. Turfgrass Soc., and ASA, CSSA, and SSSA, Madison, Wis.).
These methods all have serious drawbacks. Grass seeds require germination. As a result, sod production is relatively slow because the seeds must germinate and grow before the grass plants can root into the growth media. Also, the conditions that are most favorable conditions for seed germination may be different than the conditions for optimal growth of the grass plants. This makes the process of producing the sod difficult to automate because the environmental conditions must be adjusted after seed germination in order to maximize growth of the grass plants.
In addition, sod carpets produced from straw, finely crushed wood bark compost or secondary sewage sludge lack sufficient mechanical stability and are difficult to handle. Synthetic organic fibers may not be biodegradable and, if they do degrade, may produce toxic by-products. Soilless sod prepared from flax fibers as disclosed by Baron appears to require the use of polystyrene marbles to provide sufficient aeration for the germinating seeds. These polystyrene materials may suffer from the same drawbacks as synthetic organic fibers noted above.
Accordingly, there remains a need for a soilless sod which overcomes these disadvantages.
Accordingly, it is an object of the present invention to provide a soilless sod with a high degree of mechanical stability.
It is another object of the present invention to provide a soilless sod which can be prepared in less time as compared to a mat-based sod grown from grass seeds or traditional field-grown sod.
It is another object of the present invention to provide soilless sod which is composed of primarily of biodegradable materials.
It is another object of the present invention to provide a method for preparing a soilless sod having the properties described above.
The above objects and others are accomplished with a soil- and grass seed-free sod precursor containing grass sprigs and a non-woven mat made of bio-cellulosic fibers.
The objects above are also accomplished with a method of producing the sod precursor by applying grass sprigs to a soil- and grass seed-free non-woven mat made of bio-cellulosic fibers.
The above objects are also accomplished by a method of producing a soil-free sod by applying grass sprigs to a soil- and grass seed-free non-woven mat made of bio-cellulosic fibers and providing the sprigs with essential nutrients and water.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description.
The present invention is directed to a soilless sod in which a soil- and grass seed-free non-woven bio-cellulosic fiber mat serves as a substrate for transplanted grass sprigs. The term xe2x80x9csodxe2x80x9d as used herein refers to a grass turf held together by intermeshed grass roots and mat fibers.
The terms xe2x80x9csoillessxe2x80x9d and xe2x80x9csoil-freexe2x80x9d as used herein refer to a sod and a mat which are substantially free of soil. The term xe2x80x9csubstantially free of soilxe2x80x9d as used herein means that the sod does not contain mineral soil as a growth medium. This term includes small amounts of soil that may adhere to the grass sprigs during harvesting, for example. This term explicitly excludes amounts of soil which supply the grass sprigs with enough nutrients such that they are capable of growing without artificial nutrient sources, such as fertilizers.
Applying the grass sprigs to the mat produces a soilless sod precursor, i.e., a composition containing the sprigs and the mat which is not held together by intermeshed roots and mat fibers. A sod is produced after the sprigs have grown into the mat.
A grass sprig is generally recognized to include a stolon. A stolon (also known as a runner) is a grass stem that grows horizontal to and above the surface of the ground. A stolon may contain one or more nodes from which roots will grow. Some of the nodes may have roots when the sprig is harvested. A sprig may also be a rhizome, which is generally recognized as a grass stem that grows under the surface of the soil.
The term xe2x80x9cgrass sprigxe2x80x9d as used herein excludes grass seed. Sprigs are distinguishable from seeds in terms of gross biological morphology and genetic composition. In terms of morphology, grass seeds contain the plant embryo and a food source enveloped in a protective seed coat. In contrast, sprigs are not grass plant embryos and do not contain seed coats. Genetically, every grass seed collected from the same mother plant is different because a seed is the product of sexual reproduction. In contrast, sprigs harvested from the same mother plant will all be substantially the same genetically because they are clones of the mother plant. Therefore, sod grown from grass sprigs is distinguishable from sod prepared from seeds. In a sprig-grown sod, the individual grass plants will be substantially identical genetically. In contrast, each grass plant in a seed-grown sod is genetically different. Determining whether the grass plants in a sod are genetically the same or different may be accomplished using DNA fingerprinting techniques well-known to those of skill in the art. For example, see G. Caetano-Anolles, L. M. Callahan, P. E. Williams, K. R. Weaver and P. M. Gresshoff, DNA Amplification Fingerprinting Analysis of Bermudagrass (Cynodom): Genetic Relationships between Species and Interspecific Crosses, Theor. Appl. Getnetics 91, pp. 228-235, 1995 and K. R. Weaver, L. M. Callahan, G. Caetano-Anolles and P. M. Gresshoff, DNA Amplification Fingerprinting and Hybridization Analysis of Centipedegrass, Crop Sci. 35, pp. 881-885, 1995, both incorporated herein by reference.
The sod precursor is substantially free of grass seeds, as well as products that result from degradation of grass seed following germination (such as seed hulls). As used herein, the term xe2x80x9csubstantially free of grass seedsxe2x80x9d means that the sod may contain a very small number of seeds that may be collected when the grass sprigs are harvested from the mother plant, for example. The sod of the present invention excludes a grass-fiber mat composition that is grown predominantly from grass seeds. It is to be understood that the sod produced from the precursor may contain seeds, because the mature grass plants growing on the mat may produce seeds.
After the sprigs are applied to the mat, roots and lateral stems (stolons and rhizomes) grow from the nodes and into the upper surface the mat. At least a portion of the roots, stolons and/or rhizomes form an intermeshed network on the upper surface of the mat. In addition, at least a portion of the roots may grow into the mat. Preferably, a significant portion of the roots grow into the mat. At least a portion of the roots in the mat will intermesh with each as other and the fibers of the mat. These intermeshed networks of grass plants and mat fibers afford a sod carpet with significant mechanical strength. A portion of the roots may grow through the mat and form a network on the lower surface of the mat, which further increases the mechanical stability, particularly the shear strength, of the sod. After growth is complete, the sod may be rolled up, transported and applied to a soil substrate. Once applied, the sod grows into the soil substrate to produce a lawn.
The term xe2x80x9cnon-wovenxe2x80x9d refers to a mat comprising bio-cellulosic fibers that is produced by a method other than weaving. Non-woven fiber materials are discussed in Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, Volume 10, pages 546-547, incorporated herein by reference.
The term xe2x80x9cbio-cellulosic fiberxe2x80x9d is defined herein as a naturally occurring fiber which is isolated from a plant and which contains cellulose. Bio-cellulosic fibers are also known as vegetable fibers. This term includes fibers that may be processed, e.g., retted, boiled and/or bleached, after isolation from the natural source. Bio-cellulosic fibers include regenerated cellulose fibers, such as rayon. This term does not include natural cellulose-based fibers which have been transformed by covalent chemical modification, such as cellulose esters (e.g., cellulose acetates) or synthetic organic polymers, e.g., acrylic polymers, polyesters, polyamides, etc. It is to be understood that while the term xe2x80x9cbio-cellulosic fiberxe2x80x9d does not include cellulose esters or synthetic organic polymers, the mat may contain these materials in addition to the bio-cellulosic fiber. Bio-cellulosic fibers are extensively discussed in Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, Volume 10, pages 727-744, incorporated herein by reference in its entirety.
The bio-cellulosic fiber may be a bast fiber (also known as a stem fiber), leaf fiber (also known as a soft fiber) or a seed-hair fiber. Bast fibers include kenaf, roselle, flax, hemp, Chinese jute, jute, ramie, Sunn hemp, and nettle. Leaf fibers include abaca, phormium, sisal, cantala, caroa, henequen, istle, Mauritius, hesperaloe, New Zealand flax and sansevieria. Seed-hair fibers include coir, cotton and kapok. Preferably, the mat comprises bast fibers. Kenaf and roselle fibers are particularly preferred. Kenaf is most preferred. The mat may contain a mixture of different bio-cellulosic fibers, i.e., the mat comprises at least one type of bio-cellulosic fiber.
The bio-cellulosic fiber preferably contains at least 40 wt % cellulose, more preferably at least 75 wt %, even more preferably 85 wt % and most preferably at least 95 wt % cellulose. These ranges of cellulose content in the fiber explicitly includes all specific values and subranges therebetween, including at least 45, 50, 55, 60, 70, 80, 85, 90, 91, 92, 93 and 94 wt % cellulose. The fiber may also contain 0 to 50 wt % of lignin, 0 to 25 wt % of pectins, 0 to 25 wt % of hemicellulose and 0 to 10 wt % of other extractives. These ranges for the lignin, pectins and other extractives in the fiber explicitly include all specific values and subranges therebeteen.
The mat may contain 40 to 100% by weight of the bio-cellulosic fiber. Preferably, the mat contains 45 to 100%, more preferably 50 to 100%, even more preferably 75 to 100% and most preferably 95 to 100% by weight of the bio-cellulosic fiber, based on the total weight of the mat. In a particulary preferred embodiment the mat contains 100% by weight of the bio-cellulosic fiber. These weight percent ranges explicitly include all specific values and subranges therebeteen, including 55, 60, 65, 70, 80, 90, 97 and 99% by weight. It is to be understood that these weight ranges refer to the dry weight of the mat before grass sprigs are applied, i.e., these ranges are based on the total weight of the mat only.
The mat may contain other materials in addition to the bio-cellulosic fiber. The mat may contain other types of fibers, such as wood fibers or synthetic organic fibers. Wood fibers may increase the water retention of the mat. Examples of organic fibers include acrylic, cellulose ester (such as cellulose acetates), elastomeric, olefin, polyester, polyamide (such as nylons) and poly(vinyl)alcohol fibers. A detailed description and specific examples of synthetic organic fibers is provided in Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, Volume 10, pages 539-726, incorporated herein by reference in its entirety. A synthetic organic polymer may function as a binder agent. The mat may also contain non-fibrous polymers, such as polysaccharides (such as starch), proteins, polyacrylamide and other water-retention agents.
The weight of the mat may vary widely to accomodate plant species differences. The mat may have a weight of 100 to 1200 g mxe2x88x922. Preferably, the weight is 200 to 1400 mxe2x88x922, more preferably 250 to 1200 g mxe2x88x922 and most preferably 500 to 1100 g mxe2x88x922. These weight ranges explicitly include all specific weight values and subranges therebetween, including 150, 300, 325, 400, 600, 650, 700, 800, 900, 975 and 1000 g mxe2x88x922.
The mat may comprise one or more individual layers of fiber material. One to four layers is preferred. Multiple layers are preferably stacked directly on top of each other. The individual layers may be lightly stitched together (e.g., spun woven) to facilitate handling. The total thickness of the mat is not particularly limited. The total thickness is preferably 0.1 to 1 inch, more preferably 0.2 to 0.9 inch, even more preferably 0.4 to 0.8 inch and most preferably 0.5 to 0.8 inch. These mat thickness ranges include all specific values and subranges therebetween. The length and width of the mat are not particularly limited. Preferably, the mat has a length and width which makes it easy to roll and transport before applying the sprigs and after production of the sod turf. A particularly preferred size is 1 m wide and 15 m long.
The mat is preferably biodegradable. The term xe2x80x9cbiodegradablexe2x80x9d means that the mat will degrade when the sod is applied to a soil substrate. Preferably, the mat is made of materials that have a fertilizing effect on and/or are non-toxic to the grass during decomposition. It is to be understood that time required for biodegradation depends on many environmental variables, including the time of year the sod is applied and local weather conditions (temperature and the relative amounts of sunlight, rain, etc.). Biodegradation preferably takes 6 to 18 months.
The mat may be prepared by techniques well-known to those of skill in the art. Commercial producers utilize xe2x80x9cline productionxe2x80x9d of an air-laid web. Fiber is fed to a opener, blown to a mixer and then blown to a RANDO Webber. The webber blows out a web of fiber onto a chain belt which immediately passes under a roller and into an oven. The oven sterilizes the fibers and melts the binding agent. Additional rollers compress the hot mat to a uniform thickness. As the mat cools, it is cut and rolled to the appropriate length. Mats may also be made by floating an appropriate weight of fiber on water in a tank having a wire screen, transferring the fibers to the screen by removing the screen from the tank and then drying the resulting fiber mat. Examples of other suitable mats are disclosed in U.S. Pat. No. 4,364,197. The preferred kenaf mats are available commercially as a 100% kenaf mat from Mississippi MAT-Line/Agro-Fibers, Inc. (Charleston, Miss., USA) or Mat Inc. (Floodwood, Minn., USA).
The grass sprigs are not particularly limited. Preferably, the sprigs are of grass varieties that are recognized as useful for athletic fields, golf courses and/or residential or commercial lawns. The sprigs may be of a warm or a cool season grass. Non-limiting examples of warm season grasses include bahaigrass [Paspalum notatum Flugge.], bermudagrass [Cynodon dactylon (L.) Pers. xe2x80x98Commonxe2x80x99; C. dactylon x C. transvaalensis Buritt-Davy xe2x80x98Tifwayxe2x80x99, xe2x80x98Tiffgreenxe2x80x99, xe2x80x98Tidwarfxe2x80x99; C.x magenissi Hurc. xe2x80x98MS Expressxe2x80x99], buffalograss [Buchloe dactyloides (Nutt.) Engelm.], centipedegrass [Eremochloa ophiuroides (Munro.) Hack. xe2x80x98Commonxe2x80x99], St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze xe2x80x98Raleighxe2x80x99], zoysiagrass [Zoysia japonica Steud. xe2x80x98Meyerxe2x80x99 and xe2x80x98Sunrisexe2x80x99]. An example of a cool season grasses is creeping bentgrass [Agrostis stolonifera var. palustris]. The warm season grasses are preferred.
In a particularly preferred embodiment, the sprigs are of a warm season grass that is incapable of reproducing by seeds, i.e., a sterile grass or ones with poor seed germination. A sterile grass may have a seedhead, but produces no viable seed. Sterile grasses are well known to those of ordinary skill in the art. For example, many of the improved varieties of bermudagrass are sterile. Zoysiagrass is preferably established by sprigs because seed germination is extremely poor ( less than 3%). A soilless sod containing these grasses can only be made from sprigs. The sod may contain sprigs of a single grass variety. Alternatively, a mixture of sprigs of different grasses may be used.
The sprigs may be obtained using techniques well-known to those of skill in the art. For example, the sprigs may be harvested from field plots with a vertical mower (dethatcher). Suitable sprig harvesting apparatus are described in U.S. Pat. Nos. 5,528,890, 5,417,293, 3,589,319 and 3,939,785, all of which are incorporated herein by reference. After harvesting, the sprigs are preferably kept moist and cool and away from direct sunlight. Preferably, the sprigs are planted within 24 hours after harvesting, and more preferably, sooner. Sprigs may also be obtained commercially, for example from MS Grass Nursery (Hattiesburg, Miss. USA) and Rainey Sod Farm (Corinth, Miss. USA).
The sprig density on the mat is preferably chosen to produce rapid coverage of the mat and minimize sprig crowding during growth. The sprig density may be 0.05 to 1.5 m3 arexe2x88x921. Preferably, the sprig density is 0.1 to 1.2, more preferably 0.25 to 0.9 and most preferably 0.25 to 0.75 m3 arexe2x88x921. These ranges include all specific values and subranges therebetween.
The sod may be prepared by applying the grass sprigs to the upper surface of the mat using techniques well-known to those of ordinary skill in the art. For example, commercial row planters may be used drop the sprigs on the surface of the mat, see R. Jensen, Planting a Large Turf Area, Proc. Of the Univ. Of Florida Turfgrass Management Conference: 8, pp. 130-132, 1965.
After application, the sprig roots grow into the mat as described above. Since the mat contains substantially no soil, the sprigs should be provided with essential nutrients and water. Of course, grass is a green plant and requires light for growth. The amount of light required may vary depending on the grass variety, as is well-known to those of skill in the art. Essential nutrients may be provided using any of the fertilizers well-known to those of ordinary skill in the art. Suitable fertilizers are disclosed in U.S. Pat. No. 4,941,282 (column 2), 5,224,292 (column 3), 4,364,197 (column 5) and 5,224,290 (column 7), all incorporated herein by reference. Preferably, the fertilizer is a mixture of water-soluble and slow-release fertilizers. Nitrogen gas may also be applied in addition to fertilizer. Water is preferably provided to the growing sod carpet on an as-needed basis to prevent dessication. Other water-soluble adjuvants may be used in combination with the fertilizer, such as other nutrients, fungicides, algicides, weed killers, pesticides, etc. Suitable examples of water-soluble adjuvants are disclosed in U.S. Pat. No. 5,224,292, column 3-4, incorporated herein by reference. Since all of the nutrients may be supplied by a fertilizer, the soilless sod preferably excludes, i.e., is substantially free of composted materials (such as crushed bark and mushroom media), animal waste, mulch and sewage materials. The sod also preferably excludes, i.e., is substantially free of, non-biodegradable organic compounds, such as polystyrene marbles (such as those disclosed in U.S. Pat. No. 4,364,197, column 2), and mineral soil additives, such as sand, vermiculite and perlite.
After sprigging the mat, a scrim is preferably placed over the sprigs. The scrim layer increases the relative humidity around the sprigs and helps weigh them down into the mat, thus preventing them from moving off the mat. The scrim layer may also protect the sprigs from sunburn and/or dessication. The scrim layer is preferably translucent and/or biodegradable. Preferably, the scrim is light-colored and, more preferably, white. The scrim layer may be made of any suitable material. A biodegradable material is preferred. A scrim that degrades in 7 to 30 days is particularly preferred. A regenerated spun cellulose fiber scrim is particularly preferred. A rayon scrim is particularly preferred. The scrim layer preferably has a maximum thickness of 1 mil.
The sprigged mat is preferably grown over a root-impervious surface. This surface may also be water-impervious. The root-impervious surface may encourage the roots that grow through the mat to form an intermeshed network on the lower surface of the mat. Non-limiting examples of the root-impervious surface include plastic, concrete and asphalt. A plastic layer is preferred. The thickness of the plastic layer is not particularly limited. A preferred thickness is 2 to 10 mil.
The sprigs are allowed to grow until the desired level of mat coverage is achieved. The time required to reach the desired level of coverage will, of course, vary with the type of grass used and the growing condition, for example. Preferably, mat coverage is achieved in 3 to 20 weeks, more preferably 4 to 20 weeks and most preferably 5 to 18 weeks.
After growth is complete, the sod is a lightweight carpet of grass turf, which is easily rolled and transported. The sod may be applied on top of a soil substrate. The sod is preferably removed from the root-impervious layer before application to the soil substrate. The nature of the substrate is not particularly limited. Preferably, the substrate is a bare plot of soil. Particularly preferred substrates include athletic fields, golf courses and commercial and residential lawns. After application, the roots of the sod grow into the soil substrate to produce a lawn.